July-August, 2007

How Much Fertilizer Shall I Use? - from USDA Leaflet No. 307. (A Gardener's Guide for Converting
Tons or Pounds Per Acre into Pints, Cups, Tablespoons,
or Teaspoons per Row or Plant)

How to calculate small measures of fertilizers
from recommended applications by weight for large areas

Books and bulletins on agriculture and gardening usually give recommendations
for the use of fertilizers and lime in tons or pounds per acre, or in pounds
per thousand or hundred square feet. The gardener often finds difficulty
in converting these weights into the measures needed for a small plot or
for a single row or a single plant; and frequently he has no scales for
weighing. This folder makes the conversions for him, using the common household
measurements of pints, cups, tablespoons, and teaspoons.

For example, if 300 pounds of superphosphate or mixed fertilizer are
recommended per acre, you will find by turning to table 1 that this means
7 pounds per thousand square feet, or 11 ounces (1 1/2
cups) per hundred square feet. Then, turning to table 2, you will find that
1 1/2 cups per hundred square feet means 1/2
cup for each 10-foot row if the rows are 3 feet apart, or 6 tablespoonfuls
for each plant if the plants are spaced 5 x 5 feet. A large number of such
conversions are given for various kinds of fertilizer material and to fit
various needs.

Table 3 shows volume measures (in cups, tablespoons, etc.) of chemicals
to be added to each bushel of plant material in making a compost pile, based
on directions in weight per ton of plant material.

The rates to be selected for the various materials depend on the soil
and its previous treatments and the requirements of the plants. Certain
materials- ground limestone, where needed, and superphosphate- are used
in relatively large quantity; borax and others, sparingly. For example,
small-rate supplemental additions of ammonium nitrate can be given tomatoes
with advantage, whereas very much would injure the plants.

The values tabulated are near enough for all practical purposes, though
they are only approximate, since the weight of a given volume of a material
will vary with its moisture content and texture. In making the calculations
it was assumed that the materials will be scooped up into the container
without any packing, and that they will be loose and not lumpy. The standard
pint, cup, tablespoon (tbs.), and teaspoon (tsp.) are used for liquid measure.
Other than for liquids, level-full measures are understood, with two exceptions:
Slightly heaped (indicated by h); and a trifle less than full (by s).

For materials not included in the lists, one may weigh carefully a full
pint and determine approximately the group to which it belongs.

It will be useful to remember (1) that a pint of water weighs just a
little more than a pound (actually, 1.046 pounds); (2) that an acre is equivalent
to 43,560 square feet (a plot about 209 feet square); and (3) that a pint
is equivalent to 2 cups, or 32 tablespoons, or 96 teaspoons.

Table 1. Weights of various fertilizing materials per acre, per 1,000
square feet, and per 100 square feet and the approximate equivalent-volume
measures for 100 square feet, grouped according to weight in comparison
with that of water.

Materials

Weights Specified per --

Volume Measure for 100 Sq. Ft.

Acre

1,000 Sq. Ft.

100 Sq. Ft.

Pounds

Pounds

Pounds

Pints

Weight about the same as that of water
Examples: Cal-Nitro (or A-N-L), manure salts.

Weight about 6/10 that of water
Examples: Cottonseed meal, sulfur, fish scrap.

1,300

30

3

5

545

12 1/2

1 1/4

2

Ounces

260

6

10

1

Cup

130

3

5

1

Pounds

Pints

Weight about 5/10 that of water
Example: Hydrated lime.

1,100

25

2 1/2

5

435

10

1

2

Ounces

220

5

8

1

Cup

110

2 1/2

4

1

Manure (moist):

Tons

Pounds

Bushels

Loose

13

600

60

2

Packed

13

600

60

1

Dry straw or leaves packed tightly with hands

5

250

25

2

Table 2. Approximate equivalent-volume measures of materials to use in the
row and per plant at various rates per 100 square feet.

Rates per 100 Square Feet

Rates per 10 feet, Rows Spaces --

Rates per Plant, Spaced --

3 ft.

2 ft.

1 ft.

5 x 5 ft.

2 1/4 x 2 1/4
ft.

2 x 1 ½ ft.

Pints

Pints

Pints

Pints

Pints

Cups

Cups

10

3

2

1

2 1/2

1

1/2

Cups

Cups

Cups

Cups

6

3 1/2

2 1/2

1 1/4

3

(h) 1/2

(h) 1/4

5

3

2

1

2 1/2

1/2

1/4

Tbs.

Tbs.

4

2 1/2

1 1/2

3/4

2

6 1/2

(h) 3

3

1 3/4

1 1/4

(h) 1/2

1 1/2

5

2 1/2

2 1/2

1 1/2

1

1/2

1 1/4

4

2

Tbs.

2

1 1/4

3/4

6 1/2

1

3 1/4

1 1/2

1 1/2

(h) 3/4

(h) 1/2

5

3/4

2 1/2

(h) 1

Tbs.

Tsp.

1

1/2

6

3 1/4

1/2

1 1/2

2 1/2

Cups

Tbs.

1 1/2

1/2

5

2 1/2

6

1

1 1/2

Tbs.

Tsp.

1

5

3 1/4

1 1/2

4

2 1/2

3/4

1/2

2 1/2

1 1/2

3/4

2

1 1/4

1/2

Tbs.

Tsp.

Tsp.

4

1 1/4

2 1/2

1 1/4

1

1/2

1/4

Tsp.

1

1

(h) 1/2

1/3

1/4

1/6

1/12

Bushels

Bushels

Pecks

Quarts

Bushel

Quarts

Quarts

2

(h) 1/2

1 1/2

6

1/2

3

1 1/2

Peck

Peck

1

(h) 1

(s) 1

3

1

1 1/2

3/4

h=Slightly heaped.

s=A trifle less than full.

Measuring Chemicals for Compost Heaps

In making compost heaps with oak leaves as the chief source of organic
matter, together with some grass and other plant materials, chemical aids
are needed to disintegrate the more durable parts. If, however, a considerable
quantity of lawn clippings and other plant tissue is used, the weight or
measure of the chemicals named in table 3 may be somewhat reduced. When
manure constitutes half the organic matter, no nitrogen is required-only
the phosphate and limestone are needed. No limestone should be used if materials
are to be applied to blueberries, azaleas, or similar acid-loving plants.

The compost may be prepared in layers, a layer of garden soil or dark-colored
surface soil out of the woods about ½ to 2 inches thick, alternating
with each 6- or 12-inch layer of fresh organic matter. When finished, the
whole should be covered with 2 to 4 inches of soil.

Table 3. Volume measures of chemicals to be added separately to each
bushel of plant material in making a compost pile, at specified rates per
ton of material.

Chemicals

Weight Needed per Ton of Material

Volume Measure Needed per Bushel of Material 1

Pounds

Cups

Method 1:

(a)

Either ammonium sulfate

80

1

or ammonium nitrate

50

1/2

(b)

Either ground dolomitic limestone 2

60

2/3

or wood ashes 2

80

1 1/2

(c)

Superphosphate

50

1/2

Tbs.

(d)

Magnesium sulfate (Epsom salts) 3

8

1

Method 2:

Cups

(a)

Mixed fertilizer 5-10-5

300

3

(b)

Ground dolomitic limestone 2

60

2/3

1 Packed tightly with the hands.

2 For acid compost omit lime, limestone, and wood ashes.

3 Epsom salts to be added only if dolomitic limestone is unavailable
and ordinary limestone is used (at same rate).

Issued by Washington State University Cooperative Extension, and the U.S.
Department of Agriculture. Reprinted from USDA Leaflet
No. 307. Published May 1982.